A three-dimensional channel is widely found in key components of engines, steam turbines, centrifugal pumps, compressors, and similar power equipments such as impellers and turbochargers. Common machining methods for three-dimensional open channels include mechanical cutting, electrical discharge machining, and electrochemical machining.
A mechanical cutting method mills material by means of multi-pass flank milling, plunge milling, or turning and milling compound machining with end mills in accordance with characteristics of the flow channels. Mechanical cutting achieves comparatively good machining efficiency for low hardness material. However, it causes low efficiency and serious tool wear for flow channel machining for difficult-to-mill material, and in some case, normal milling is out of question for three-dimensional flow channels with complex geometry due to interference. Electrical discharge machining is apt to achieve comparatively good surface quality and accuracy, but it has the down side of limited efficiency, which is a major issue for electrical discharge machining of three-dimensional flow channels.
Efficiency is also an issue for electrochemical machining. See, “A step-wise digitally controlled electrochemical machining process for an impeller and key techniques therefor,” Journal of South China University of Technology (Natural Science Edition), 38(8), 2010: 71-77. The reference discloses an electrochemical machining method with a direct current voltage of 12V, 20% of NaNO3 as electrolyte, working pressure of 0.8 MPa, and feed rate of 2 mm/min. As seen from the processing parameters, the electrochemical machining method involves a slow electrolysis process, has low feed rate, and creates heavy metals and other toxic waste, thus, requires complex subsequent purification treatment.
To improve the efficiency for three-dimensional open flow channel machining, high-speed arc discharge machining may be used. High-speed arc discharge machining, as compared with traditional electrical discharge machining, has a higher energy density and a far higher material removal rate per unit time. Chinese Patent ZL201110030724.7 discloses a cluster electrode high-speed arc discharge machining method in the field of electric arc discharge machining, featuring a peak current of 635 A, suitable flushing pressure, and pulse parameters for machining of titanium alloy, with a material removal rate of 6844 mm3/mm.
Although employment of high-speed arc discharge machining attains several times higher machining efficiency, for three-dimensional open flow channels, short circuit due to poor chip removal is prone to take place and hampers normal machining operation, whether cluster electrode or other types of electrodes be employed. Further, inability of flushing holes on the tool electrode to discharge electricity results in residual bulges on the machined spots of the work-piece. Moreover, prior art three-dimensional flow channel machining proceeds in a point-wise manner, not conducive for optimization of machining efficiency.